1. Get a nice comfortable t-shirt and a tape measure.
2. Lay the shirt flat, front down.
3. Measure across the shirt where the sleeve seams meet the front and back seams.
4. Measure from the collar top to the bottom of hem.
5. Measure across the middle, a few inches below the sleeve.
6. Match your measurements to the chart & sizes.
(measurements are given in inches, centimeters in parentheses.)